Characteristics of Twinning in Marble with Stable Faulting Process

Twinning is one the micromechanisms of plastic deformation of marble. To investigate the twinning performance during faulting, shear ruptures with different deformations were induced in Hezhou marble. Microscopic observation and quantitative analysis were performed on twinning characteristics in cross sections perpendicular to faulting plane. The results show that the twinning in the faulting zone was obviously different from that outside of the zone, presenting the characteristics of localization, kinking, thickening, bifurcation and spiking out, which is largely controlled by the relation between the shear direction and twin plane dip. Twin density of the entire sample increased slightly after loading, while twin incidence fluctuated in high level. The average twin width was not affected by loading, however, the maximum twin width increased steadily up to three times with faulting deformation. The above results show that under low confining pressure, the twinning of Hezhou marble is unobvious overall, but concentrated in the shear zone, mainly manifested by the increase of the width of the twin. The apparent characteristics of twinning are controlled by the relative relationship between the shear direction and the inclination of the twin lamellae.